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== Measuring the DAC == The [https://www.amd.com/system/files/TechDocs/33234H_LX_databook.pdf AMD Geode LX Processors Data Book] explains that after video has been rendered it's output through an 8-bit DAC. The following signals are used by the DAC: * DVREF - A 1.235V voltage reference * DRSET - A 1.21K current setting resistor * DAVdd - Four 3.3V analog power connections * DAVss - Four 0.0V analog ground connections * RED, GREEN, BLUE - Analog DAC output * DOTREF - 48MHz input clock After looking at the [https://wiki.laptop.org/mediawiki/images/8/83/XO-1_Schematics.pdf OLPC XO-1 Schematics] and [https://manualzz.com/doc/29656964/amd-geode%E2%84%A2-lx-epic-rdk-reference AMD Geode LX EPIC RDK Schematics] which both use LX processors and inspecting the PCM-9375 board itself I figured out the following: * The OLPC XO-1 uses a resistor voltage divider to generate DVREF * The AMD EPIC RDK and PCM-9375 use a LM4041AIM3-1.2 to generate DVREF * The OLPC XO-1 sends the DAC signals to the connector directly * The AMD EPIC RDK and PCM-9375 put inductors and ESD protection in front of the signals * The PCM-9375 has some capacitors in front of the signals * The OLPC XO-1 and AMD EPIC RDK connect the DOTREF to the CS5536 chip * I presume the PCM-9375 does that too Most of the signals above are physically exposed balls under the Geode chip. Probing them shows: * DVREF hangs around 1.22V * DAVdd hangs around 3.3V * DOTREF is a 48MHz sine wave (possibly scope artifacts) Everything looks fine here.
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